"It's just a very silly show," The Origin Of Species' producer confided in me when I met her in the Pleasance bar. She's right; it's one of the sillest shows I've seen this year, and I mean that in an entirely positive way. The silliness begins with the Fringe programme's longest title, which, for form's sake, I'll use in full just once: The origin of species by means of natural selection, or the survival of (r)evolutionary theories in the face of scientific and ecclesiastical objections: being a musical comedy about Charles Darwin (1809-1882).

Behind the momumental moniker stands a gleeful romp through Darwin's life story, which respects his work but refuses to take it too seriously. You'll find Darwin waiting for you as you file into the overgrown Portakabin which is the Pleasance Beyond; he greets you with genial surprise, as though he'd somehow forgotten he'd invited these hundred-odd people for tea. It's the start of a witty and engaging one-hour monologue, in which John Hinton enjoys his role as Darwin - sharing his life, work, and love of barnacles.

The life story's at the Shakespeare In Love end of the accuracy scale - but that, of course, is the point. By imagining for example that Darwin's uncle Wedgewood, as well as making pots, smoked it, Hinton both opens the door to some fine characterization and helps along the narrative of Darwin's (real) life. The script is sparkling and charming enough that I forgave the wilfully appalling puns, and the final moments do a great job of pulling the strands together - watch out in particular for the memorable visualization of the sudden explosion of Darwin's success.

And then, there's the musical bit. In this parallel version of Darwin's life, theories are written as musical score, and the great man himself learned just two things at school: Latin, and classical guitar. It's incumbent on me to point out that Mr Hinton can't really sing, but it doesn't actually matter. The musical numbers work surprisingly well, even though - or, more likely, because - the rhymes and metre are are gratuitously poor.

But the greatest surprise of all is that this show is educational too. Summarizing the whole of Origin Of Species as a patter song was over-ambitious, perhaps, but the entertaining demonstrations involving members of the audience were both informative and fun. The audience interaction is very well-done; everyone gets involved, nobody's singled out too much and the banter is natural rather than forced. I don't quite remember which type of finch Darwin declared I was, but I do remember being secretly pleased.

I've heard some people complain this is really a kids' show, but it didn't feel that way to me. The children in the audience seemed to enjoy it, yes, but so did I; perhaps we should call it a family show, where the kids are strictly optional. In any case, if you want a show with a big title and a big heart to loosen your funny bone for a Fringe afternoon, the charming Origin Of Species... is the natural selection.